The threat of an oil shortage has created a new shortage in the Washington area -- diesel-powered cars, auto dealers said yesterday.

"I just can't handle any more (new orders)," said Dave Murray of Cavalier Cars Inc., an Arlington volkswagen dealership that stopped taking orders on Saturday for its diesel Rabbits. "The waiting list would have gotten up to 100 names."

Other area dealers said it can take up to six months to get delivery on a diesel-powered car -- which burn cheaper fuel than gasoline-powered cars and get better mileage than most gasoline-powered automobiles.

"If you watned to order one right now, I'd have to tell you to order a 1980," said Maury Graham of Farrish Oldsmobile, a Fairfax County dealership that learned last week its allocation of 1979 diesel Oldsmobiles and Cadillacs has run out.

"Diesel sales have picked up considerably sine this Iran thing," said Charles Kurtz of Midtown Motors Inc., a D.C. Peugot dealership, "They're getting scarce."

Political upheaval in Iran, which has interrupted oil shipments from that major Middle East supplier, prompted President Carter two weeks ago to plead with Americans again to conserve fuel. Many drivers, with sour memories of the 1973 Arab oil embargo that led to long lines at gasoline stations, appear to be responding by buying diesel cars -- or trying to buy one.

The shortage in Washington is part of a national boom in diesel sales in recent weeks. "We just can't supply the demand," said Baron Bates, an executive of Volkswagen of America Inc. in Englewood Cliffs, N.J., which expects to sell 80,000 diesel Rabbits and Dashers in the United States this year. Bates says even he cannot tell how high the demand will be.

Car dealers say diesels, in comparison to gasoline-powered cars, get anywhere from an average of six miles more per gallon in an Oldsmobile Cutlass to 15 miles more per gallon in a VW Rabbit. Diesel fuel generally is 6 cents or 7 cents cheaper per gallon than gasoline.

There is a catch. Diesel fuel is hard to find in many urban areas, and diesel cars cost more -- $5,783 for a basic diesel-powered Rabbit versus $5,097 for a similar gasoline-powered model. With a diesel there are only five makes to choose from -- Volkswagen, Peugeot, Mercedes, Oldsmobile and Cadillac.

In Arlington, Murray said he is trying to get his 1979 allocation of VW diesels increased. He concedes it probably will not be possible because the diesel Rabbits come from Europe, unlike regular Rabbits which are now manufactured in Westmoreland, Pa.

Privately, some area dealers said yesterday they have had to restrain their salesmen from promising delivery on diesels. The salesmen have begun to stress in their sales spiels that diesels cost more -- from $300 to $2,000, depending on the make of car.

"You're welcome to come by and look at a car," one salesman told a prospective customer yesterday at a VW dealership. "Providing, of course, you'd be interested in a regular gasoline engine."

Volkswagen dealers like Robinson admit they might be able to come up with a diesel Rabbit in two months, but not necessarily to the specificiations of the buyer. Increasingly, dealeers say, they are demanding $500 deposits from customers just for the privilege of being on the waiting list -- if they have one.

"It used to be that people would say gas would just be a few cents more," said A1 Lewis, sales manager at McNey Motors Inc., a D.C. Mercedes-Benz dealership where seven out of 10 cars sold are diesels, more than double last year's rate. "Now people are asking whether gas will be there at all," Lewis said.

Industry experts note that diesel engines can run, at least in theory, on No. 2 home heating oil. Auto dealers, however, say it probably hurts the engines and fuel companies point out that it is against the law unless the car owner pays state and federal road fuel taxes on the heating oil.

Car dealers, meanwhile, say they find themselves in a bind. "It's very frustrating to have a product like this and not be able to get enough," says Murray.